It is known to ablate material from a target by rotating the target while directing a beam or pencil of radiation from a laser onto the target material, thereby vaporizing same.
In our above-identified copending application, an apparatus which makes use of the ablation of material from a target in this manner is described. That apparatus comprises an ultrahigh-vacuum chamber (UHV chamber) and serves for the stoichiometric reproduction of the material of the target as a coating on a substrate, i.e. the formation on a substrate of a coating at the exact composition of the target material which is used.
In that system, a plasma is generated from the target material by directing the beam from an excimer laser against the target. The rectangular beam profile is focused to a line by a cylindrical lens.
This system is able to effect relatively high coating rates with stoichiometric reproduction of the target composition. The target is rotated and the focuse laser beam is directed against the disc-shaped face of the plate-like target.
While a homogeneous ablation of material can be initially achieved in this manner, experience has shown that the method gives rise to crater formation at the target center which can reduce, on the one hand, the life of the target and on the other hand detrimentally effects the homogeneity and reproducibility of the process.